code: def change_observation(obs, obs_space):
      # convert all images to a 3d array with 1 channel
      obs = obs[..., None]
      return obs
  
file_path: ray/rllib/tests/test_pettingzoo_env.py
imports: from numpy import float32
  from pettingzoo.butterfly import pistonball_v6
  from pettingzoo.mpe import simple_spread_v3
  from supersuit import color_reduction_v0, dtype_v0, normalize_obs_v0, observation_lambda_v0, resize_v1
  from supersuit.utils.convert_box import convert_box
  import unittest
  import ray
  from ray.rllib.algorithms.ppo import PPOConfig
  from ray.rllib.env import PettingZooEnv
  from ray.tune.registry import register_env
label_desc: Use image node_id 1 for calling a global function with example usage: change_observation(obs, obs_space) and returns: obs